In recent years, use of combustionless, heat-pump type water heaters (e.g., EcoCute (registered trademark)) has been widely spread in industry and ordinary household as measures for reduction of CO2, which is assumed to be a ringleader of the global warming. In addition, fuel cells (e.g., ENE FARM (registered trademark)) by Tokyo Gas Co., Ltd.), which are new energy systems extracting hydrogen from gas and generating electricity. In the above new water heaters, heat exchange from cold water to warm water is necessary, and the heat exchanger using the meandering type copper pipe illustrated in FIG. 8(a) is generally known.
As illustrated in FIG. 10, the conventional pipe bending machine 90 includes a support roller 92, a bending roller 93, and a chuck 94. A groove having the shape of a semicircle is formed on the outer circumferential surface of the support roller 92 in such a manner that a pipe can be inserted through the groove. Another groove having the shape of a semicircle is formed on the outer circumferential surface of the bending roller 93, and the bending roller 93 is supported in such a manner that the bending roller 93 can be turned around a center of rotation, which is the center O of the support roller 92. The chuck 94 holds the pipe. When a pipe is inserted through the gap formed between the two grooves in the support roller 92 and the bending roller 93, and the bending roller 93 is turned around the center O of the support roller 92, the pipe can be bent so as to have a bend diameter identical to the diameter of the support roller 92. (See, for example, Patent Literature 1.)
As illustrated in FIG. 8(a), the characteristic of the conventional meandering type heat exchanger pipe is that the bend diameter of the pipe is uniformized to a single value φD. Since the conventional pipe bending machine 90 can perform only one type of pipe bending realizing the single bend diameter of φD, the meandering type pipes have been used as heat exchanger pipes until now.
However, the meandering type heat exchanger pipes as above need installation space with some extent, and it is impossible to avoid increase in the installation space in order to secure certain heat exchanger effectiveness. In addition, the future direction of the products such as water heaters is weight reduction and downsizing. Therefore, the use of the meandering type heat exchanger pipes goes against the future direction.
FIG. 8 (b) is a front view illustrating a shape of a spiral type heat exchanger pipe. The space needed for accommodation of the spiral type heat exchanger pipe having a length is approximately one-third of the installation space needed for accommodation of the meandering type heat exchanger pipe having the same length. In other words, the heat exchanging capacity which the spiral type heat exchanger pipe can achieve in a space is three times the heat exchanging capacity which the meandering type heat exchanger pipe can achieve in the same space, and therefore the spiral type heat exchanger pipe is suitable for the downsizing in EcoCute in the future.
Nevertheless, in the case where a spiral pipe is produced by bending a pipe in a conventional pipe bending machine as illustrated in FIG. 8 (b), the bend diameter is increased after every bend as D1<D2<D3 . . . <Dn. Therefore, the support roller 92 is required to be replaced after every bend is made in the pipe, so that the pipe bending operations cannot be successively performed.